1. Field of the Invention
This invention relates to gas measurement devices, and in particular to an oxygen monitor.
2. Background of the Invention
Ships are used extensively all over the world in order to transport combustible fluids in their tanks. The types of combustible fluid carried may include crude oil, refined fuel oil, etc. In order to reduce the chances of a fire occurring, oxygen present in the tanks must be pumped out before the tanks are filled with a combustible fluid. For example, in the case of crude oil, oxygen must be pumped out of the tanks until less than 8% oxygen content remains in the tank.
Normally, exhaust gasses from the ship""s main burners are used to displace oxygen-rich air from combustible fluid tanks. The exhaust gasses used for this purpose should contain less than 5% oxygen. The oxygen content of the exhaust gasses used to evacuate the ship""s tanks is monitored by means of oxygen monitors mounted on the ship""s smokestack(s). Before combustible fluids are pumped into the ship""s tanks, hand-held oxygen monitors are employed in the tanks themselves to make sure that the maximum safe oxygen percentage is not exceeded.
Existing Designs
Existing smokestack-mounted oxygen monitors typically use a vacuum pump to extract smoke samples from the smokestack, and the exhaust gasses are then pumped to a location where the monitor itself is located. There are a number of disadvantages associated with this scheme.
A first disadvantage involves calibration. this type of setup requires calibration of the. oxygen monitor every month or so. The calibration operation itself is a multi-step process which is time-consuming and expensive. Typically two calibration percentages are used (e.g. 4% and 16%); a calibration curve is fitted to these two points, then the two calibration points are re-checked to ensure accuracy. The entire process takes approximately xc2xd-1 hour of time. When the calibration process is multiplied by several monitors, and several smokestacks, over many months of operation, the time waste is considerable.
A second disadvantage involves the physical placement of the oxygen monitor. Because smoke is physically pumped from the smokestack to the location where the oxygen monitor is located, the distance from smokestack to. monitor is limited. Thus, it can be difficult to locate the monitor in a convenient place.
Accordingly, it is an object of the present invention to provide an oxygen monitor which does not require frequent calibration. Design features allowing this object to be accomplished include the use of a zirconium dioxide oxygen sensor. Advantages associated with the accomplishment of this object include the elimination of monthly monitor inspections, along with the associated cost saving,s.
It is another object of the present invention to provide an oxygen monitor whose monitor cabinet may be located remote from the smokestack. Design features allowing this object to be accomplished include a sensing assembly electrically connected to a remotely located monitor cabinet. Benefits associated with the accomplishment of this object include more convenient location of the monitor cabinet, along with the associated reduced time to view and/or maintain the monitor cabinet, and consequent cost savings.
It is another object of the present invention to provide an oxygen monitor which requires no suction pump to bring exhaust gasses from the smokestack to the oxygen sensor. Design features allowing this object to be accomplished include an intake tube mounted within an exhaust tube, a pressure differential caused by exhaust gas flow between an intake tube mouth and an exhaust tube mouth, and a heated oxygen sensor. Benefits associated with the accomplishment of this object include simpler design with less required components, and hence reduced necessity of maintenance, and decreased costs.